Blank holder and die cushion cylinder having separate adjustable pressures



W. ERNST BLANKHOLDER AND DIE CUSHION CYLINDER HAVING June 6, 1944.

SEPARATE ADJUSTABLE PRESSURES Original Filed March 29, 1940 5 Sheets-Sheet 'l June 6, 1944.

w. ERN-ST 2,350,884

BLANKHOLDER AND DIE CUSHION CYLINDER HAVING SEPARATE ADJUSTABLE PRESSURES Original Filed March 29, 1940 5 Sheets-Sheet 2 igw-Zkmb I64 vim;

June 6, 1944. w. ERNST BLANKHOLDER AND DIE cusnxou CYLINDER HAVING SEPARATE ADJUSTABLE PRESSURES Original Filed March 29, 1940 5 Sheets-Sheet 3 FIB-:3

June 6, 1944. w ERNST 2,350,884

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ITIW/YEYS June 6, 1944. w. ERNST 2,350,884

BLANKHOLDER AND DIE CUSHION CYLINDER HAVING SEPARATE ADJUSTABLE PRESSURES Original Filed March 29, 1940 5 Sheets-Sheet 5 III/1.1.0457

I/VI/f/VTOP MATE? [PA 57' Patented June 6, 1944 BLANK HOLDER AND DIE CUSHION CYLIN- DER HAVING PRESSURES SEPARATE ADJUSTABLE Walter Ernst, Mount Gilead, Ohio, .assignor to The Hydraulic Development Corporation, Inc., Mount Gilead, Ohio, a corporation of Delaware Original application March 29, 1940, Serial No.

Divided and this application November 27, 1940, Serial No. 367,447

6 Claims. ('Cl. 113-45) This invention relates to presses, and in particular to hydraulic presses having blank holding arrangements in association with drawing devices.

One object of this invention is to provide a hydraulic press having a drawing plunger and a plurality of clamping cylinders which will make it possible to exert and maintain difierent pressures in the clamping cylinders, and to vary the pressure in the individual clamping cylinders independently oi! each other.

It is another object of this invention to provide a hydraulic 'press having a drawing plunger and a plurality of clamping cylinders, in which the pressure in each clamping cylinder is individually controllable and automatically maintained by means associated with said clamping cylinders.

Another object of the invention consists in providlng a hydraulic press having a drawing plunger and a plurality of individually controllable clamping cylinders in which the clamping cylinders receive their pressure fluid from a common fluid source, while each clamping cylinder has associated therewith individually adjustable pressure reducing means for automatically maintaining a desired pressure in each individual clamping cylinder.

It is a still further object of the invention to provide a hydraulic press having a drawing plunger, a plurality of clamping cylinders, and cushioning cylinders which will make it possible individually to vary and maintain the pressure in each clamping and cushioning cylinder.

These and other objects and advantages will appear more clearly from the following specification in connection with the accompanying drawings in which:

Figure 1 diagrammatically illustrates a press according to the present invention at the beginning of the downward stroke of the clamping plungers;

Figure 2 is a view similar to Figure 1, but showing the press at the end or the clamping stroke;

Figure 3 is a section along the line 3-3 of Figure 1;

Figure 4 isa section similar to Figure 3 with the exception that the pumps associated with the clamping cylinders are replaced by pressure reducing valves;

Figure 5 illustrates on a somewhat larger scale, a pump cooperating with the clamping cylinders:

Figure 6 shows a reducing valve in detail;

Figure 7 illustrates the hydraulic circuit for the cushioning cylinders: and

Figure 81s a detail of the relief valve to be used in connection with the hydraulic circuit of Figure 7.

This application is a division of my application, Serial No. 326,709, filed March 29, 1940, which has become Patent 2,294,451, Sept. 1, 1942.

The press as illustrated in the drawings comprises a bed I and a head 2 spaced from and connected with each other by strain rods 3 and nuts 4. The head 2 carries a main cylinder 5 and clamping cylinder 6. The main cylinder 5 has reciprocably mounted therein a plunger 1 carrying a press platen 8 which, in its turn, supports an upper die 9. The lower end of the main cylinder 5 is provided with packing material ill compressed by a gland l i for preventing leakage from the main cylinder. Similarly, each of the clamping cylinders 6 is provided with packing material 12 compressed by a gland 13 for preventing leakage from the respective clamping cylinder.

Through each gland I3 and packing material l2 of the clamping cylinders is passed a clamping plunger l4 carrying a blank holder i5. The press platen 8 and blank holder i5 have lugs l6 and I1 respectively through which a rod l8 with nuts l9 and 29 is passed so that the blank holder I5 is lifted by the press platen when the latter has moved a predetermined distance away irom the blank holder. The main cylinder 5 is connected at its upper end with a conduit 2| leading to one port 22 of a variable delivery pump 22, while the other port 24 of the pump 23 is connected with a conduit 25 leading to the lower end of the cylinder 5.

Each of the clamping cylinders 6 is connected by means of a conduit 25 with a conduit 21 leading to a two-way valve 29 andhaving mounted therein a check valve 29 which opens in the direction of the arrow A only. The two-way valve 28 comprises a cylinder 30 closed at its ends by packing material 3| and 32 and heads 33 and 34. The cylinder 30 has three aligned bores 35, 36 and 31 of a diameter corresponding to the diameter of pistons 38 and 39 connected with a push rod 49. The bores and 36 are separated from each other by a chamber 4! having a diameter greater than those of the pistons 38 and 39. Similarly the bores 35 and 31 are separated by a chamber 42 which has a diameter likewise greater than those ofthe pistons 38 and 39.

A conduit 43 leads from the chamber 42 to a fluid tank 44, while the conduit 21 leads into the chamber 41. The fluid tank 44 has mounted therein a valve 45 for releasing the pressure in the upper portion of the main cylinder 5 at the beginning of the return stroke of the plunger 1. w

This valve 45 comprises a casing 46 having two spring chambers. 41 and 48 and two cylinder bores 49 and 50. The cylinder bore 49 is adapted to communicate through an aperture 5| with the fluid tank, and similarly an aperture 52 is provided for effecting communication between the cylinder bore 68 and the fluid tank 44. Furthermore, a channel 63 is provided for effecting a communication between the two bores 49 and 58. A conduit 64 leadsirom the bore 58 to the conduit 2|, while a conduit 55 leads from the cylinder bore 49 to the conduit 25. A conduit 56 branches 011 from the conduit 54 and leads to the cylinder bore 49. Reciprocably mounted in.

the cylinder bore 49 is a valve member 51 with two pistons 68 and 59 which, in the position shown in Figure 1, close oif the channel 53 and the aperture 6|.

Connected with the piston 59 is an abutment 68 which is engaged by a spring 6| provided in the spring chamber 41 and urging the valve member 51 toward the right. Similarly, a spring 62 in the spring chamber 48 engages an abutment 63 connected with a piston 64 reciprocable in the cylinder bore 58. The piston 64 forms a part of the valve member 65 which carries a second piston 66. In the position shown in Figure 1, the piston 64 closes the aperture 52, while the piston 66 prevents communication between the conduit 54 and the channel 53. A conduit 61 leads from the fluid tank 44 to the port 24 of the pump 23 and has mounted therein a check valve 68 which opens only in the direction of the arrow B.

A further conduit 69 leads from the fluid tank 44 to a chamber I8 of a surge valve generally designated I I. The surge valve II has a cylinder bore I2 separated from the chamber I8 by a partition 13, and a cylinder bore I4 separated from the chamber 18 by a partition I5. The partition B is provided with a bore through which is passed a piston rod 16 carrying a piston 11. A spring I8 is mounted between the partition and the piston 11 urging the piston 11 upward. The partition 15 is likewise provided with a bore 19 which has adiameter greater than the diameter of the piston rod I6. The cylinder bore I4 has also reciprocably mounted therein a piston 88 urged by a spring 8| to its uppermost .position. In this uppermost position the piston 88 closes off a port 82 connected with the conduit 2I by a conduit 83. A conduit 84 leads from the lower part of the cylinder bore "to the conduit 54, while a conduit 85, leads from the upper portion of the cylinder bore 12 to the conduit 55.

The push, rod 48 passing'through the twoway valve 28 has adjustably mounted thereon two cams 86 and 81 having grooves 88 and 89 respectively. The cams 86 and 81 cooperate with pins 98 and 9| carried by an'arm 92 connected with the press platen 8. The arm 92 has a borev 93 through which the cams 88 and 89 may pass. The pins 98 and 9| are urged toward the bore 93 by springs 94 and 95 provided in arm 92 so that the pins may engage the groove 88 or 89 as the-case may be. The lower end of the push rod 48 is passed through-a lug, 96 connected with the bed I. The bed I carries cushioning cylinders 91 having reciprocably mounted therein cushioning plungers 98 passing through packing material 99 compressed by a gland I88 and carrying the lower die I8I.

According to the embodiment of Fig. 3, each oi the clamping cylinders 6 is connected with the pressure side of a variable delivery pump I82 by means of the conduit 26. The suction side of each delivery pump I82 is connected by means of a conduit I83 with a fluid tank I84 which, if desired. may be connected'with or form a. patio! the fluid tank 44. Branching oil! from the conduit 26 is a conduit I85 leading to a channel I86 oi the check valve 29 (see also Fig. l). The channel I86 is normally closed by a ball I88 arranged in a chamber I89 of the check valve 29. The chamber I89 communicates through a channel II8 with the chamber 4| 0! the two-way valve 28. 'As will be clear from the foregoing, the four check valves 29 prevent the pressure from equalizing in the four clamping cylinders 6, whereas the two-way valve 28 is adapted to open the clamping cylinders to exhaust.

The variable delivery pump I82, shown in detail in Figure 5, comprises a pump casing III having connected to one side thereof, for instance by means of screws I I2, a hollow arm II3. Telescoped in the hollow arm H3 is a spring casing II4 engaged by one end of the spring H5. The other end of the spring II5 abuts the wall II6 of the hollow arm II3. Reciprocably mounted within the pump casing III is a flow-control member I I1 adapted to vary the flow of the variable delivery pump by moving a secondary rotor relatively to a primary rotor. Moreover, a plurality of radial pistons and cylinders (not shown) are operatively connected with said rotors. The arrangement of these rotors and the interior of the pump is well-known to those skilled in the art and for more detailed description thereof, reference may be had to-U; S. Patents Nos. 1,964,- 244 and 2,041,172.

Threaded into or otherwise connected with the flow-control member III is an adjusting rod II 8 which passes through the pump casing III and the wall I I6 of the hollow arm I I3 and is provided with a threaded portion II9 passing through the spring casing II,4. Thethreaded portion I I9 is engaged by a nut I28 provided with a handwheel I2I so that by rotation of the handwheel I 2| in one direction, the spring casing II4 may be moved into the hollow arm II 3 thereby threaded into the flow-control member I I1; Ad-

jacent the cylinder bore I23 and adapted to communicate therewith is a bore I28 having a diameter greater than the diameter of the cylinder bore I23 and communicating through a conduit I29 with the pressure side of the pump I82. Leakage from the bore I28 toward the interior of the .pump casing III is prevented by packing material I38 provided between the pump casing III and the cylinder I22 and surrounding the push rod I21.

As will be clear from the foregoing, the spring II5 tends to hold the flow-control member in a position determined by the setting of the spring, thereby maintaining a predetermined flow of fluid of the pump I82. However, if the fluid pressure of the pump exceeds a predetermined value, this pressure will be conveyed from the pressure side of the pump through the conduit I29 into the causes the flow-control member to restrict the flow of fluid of the pump I02. In this way, the pump I02 automatically maintains the desired fluid pressure.

According to the embodiment of Figure 4, the pumps I02 are replaced by pressure reducing valves I3I which are supplied with fluid from a common variable delivery pump I42. Since this pump as shown in the drawings lacks the servomotor conduit I29 of the pump I02, provisionis made for preventing excessive pressure in the conduits between the pump I42 and the pressure reducing valves I3I. To this end a conduit I43a comprising a relief valve I42a connects the pump I42 with the tank I44. The relief valve MM is so set that it opens towards the tank I44 at a pressure slightly higher than the desired pressure in the clamping cylinders. Aside from the above mentioned features the arrangement shown in Figure 4 corresponds to that of Figure 3 and the corresponding parts are designated with the same reference numerals, however with the additional letter a.

The pressure reducing valve I3I comprises a body member I32 (see Figure 6) having reciprocably mounted therein a plunger I33 guided by a guide ring I34 and by a packing I35 preferably of U-shaped leather mounted between rings I36 and I31. A shoulder I38 on the body forms a seat for the ring I36, and a screw plug I39 threaded into the body I32 presses the ring I31 against the packing I35.

The body I32 of each of the four pressure reducing valves shown in Fig. 4 is provided with an inlet I40 connected with a conduit I03a leading to a manifold I4I which is connected with the pressure side of the variable delivery pump I42. The suction side of the variable delivery pump I42 communicates through a conduit I43 with a fluid tank I44 which may be connected with or form a part of the fluid tank 44. The inlet I40 (see Fig. 6) communicates by an inclined passage I45 and openings I46 in the ring I31 with a central chamber I41 in the end of the plunger I33. A plurality of small ports I48 radiate from the chamber I41 and pass through casing I54. The upper end of the spring I68 rests against the nut I59 while the lower end of the spring abuts the washer I49. The stem I58 is provided with a handwheel I62 by which it may be rotated, and since the nut I59 cannot rotate with the stem I58 due to the engagement of its pins I6I with the slot I56, the rotation of the handwheel will cause the nut I59 to move longi-- tudinally of the casing so as to vary the thrust the plunger. The inner end of the plunger I33 is provided with a shoulder which rests against a washer I49 which is forced outwardly by a spring I50 and therefore tends to resist the inward movement of the plunger. A chamber I5I within the body I32 communicates by means of an outlet I52 with a conduit 26a leading to the respective clamping cylinder 6a and check valve 29a. Since the clamping cylinder 6a and check valves 29a fully correspond to the clamping cylinders 6 and check valves 29 respectively, no further explanation is necessary. The ports I46 are adapted to communicate with the chamber I5I when the plunger is forced inwardly by a predetermined amount.

Screw threaded into the body I is a casing I 54 which is welded or otherwise fastened to a sleeve I55 which is preferably of non-corrosive metal. The sleeve I55 has two diametrically opposite slots I56 extending through the walls thereof a considerable distance from the outer end. A cap I51 is screw threaded on the outer end of the casing I54, and through this cap passes a stem I58 which is screw threaded on its inner end to engage a nut I59. Suitable packing I60 is provided forthe stem. Pins I6I carried by the nut I59 have their ends projecting into the slots I56 and thereby prevent relative rotation between the nut and the sleeve I55 connected with the of the spring I50. A passage I63 affords communication between the chamber I5I and the interior of the casing I54 whenthe plunger I33 is moved inwardly sufllciently to lift the washer I49 oil its seat on the body and thus open the communication, it being understood that the interior of the casing I54 is always under more or less pressure by reason of the fluid entering between the washer I49 and the sleeve I55 and around the plunger I33.

The valve opens in the following manner:

The hydraulic pressure entering through the inlet I40 and the passage I45 is supplied to the plunger I33 within the chamber I41 and also at the end of the plunger I33. This pressure being greater than that of the spring I50 moves the plunger inward. As soon as the ports I48 pass beyond the packing I35 and open communication with the chamber I5l, the fluid will pass therethrough and through the passage I63 into the spring chamber, thus affording a back pressure upon the plunger I33 in addition to the pressure of the spring I50. The pressure on the two sides of the plunger I33 will therefore tend to arrive at a balance, and it is evident that the pressure at the low pressure outlet I52 will be equal to the high pressure minus the pressure acting from the interior of the shell I55 upon the washer I49. When the pressure at the out let I52 increases, this pressure will be conveyed through the passage I63 to the interior of the sleeve I55 and act therefrom upon the washer I49 so as to move the plunger I33 downwardly, thereby restricting the flow of fluid through the ports I48 into the chamber I5I. In this way the desired pressure at the outlet I52 will be automatically maintained.

Referring now to Figure '7 illustrating the hydraulic circuit for the cushioning cylinders 91, it will be noted that each cushioning cylinder communicates through a conduit I64 with a check valve I65. This check valve I65 corresponds to the check valve I06 of Figure 3 and comprises a chamber I66 communicating through a channel I61 and a conduit I68 with the conduit I64. A further conduit I69 which may be closed by a ball I10 communicates with a conduit I1I leading into a conduit I12 which, in its turn, is connected with the pressure side of a variable delivery pump I13. The suction side of the variable delivery pump I13 is connected with a fluid tank not shown in Figure '7. The conduit I64 is also connected with a relief valve I14 shown in detail in Figure 8.

The relief valve I14 consists of a casing I15 having a bore I16 wherein reclprocates a valve plunger I11. Arranged between the valve plunger I11 and the bore I16 is a tubular member I18 having a longitudinal bore I19 and a cross bore I 80, the cross bore I communicating with an annular chamber opening into a transverse bore I8I in the casing I15. The end connection I82 of, the conduit I64 is held in communication with the bore I16 by means of a collar I83 engaging the threaded portion I84 of the casing I15, whereas a pipeconnection I85 and the transverse bore I8I.

similar to the pipe connection I82 communicates with a fluid tank (not shown) and is held in communication with the transverse bore |8| by means of the threaded collar I86 engaging the threaded portion|81 of the casing I15.

Mounted on the upper portion of the casing I15 is a tubular cap I88 secured thereto by screws I89. Within the cap I88 is a coiled spring I90, one end of which engages an enlargement I8| upon the upper end of the valve plunger I11, whereas the opposite end engages a button I82 in contact with an adjusting screw I93 threaded through a bore I94 in the upper end of the cap I88. Surrounding and covering the adjusting screw I93 is a hollownut I95 which serves to protect the adjusting screw I98 and also to lock it in its adjusted position.

As will be clear from the foregoing description, the spring I90 will normally hold the plunger I11 in such a position that the latter prevents communication between the bore I19 However, when the pressure in the bore I19 exceeds a predetermined value determined by the setting of the spring I90, the plunger I11 will be lifted to such an extent that pressure fluid from the respective cushioning cylinder 91 may pass through the conduit I64 and the bore I19 into the transverse bore I8I and from there to the fluid tank. The fluid expelled from the respective cylinder 91 cannot escape to the conduit I1I since the communication between the conduit I68 and the conduit I 1| is closed by the ball I10.

The operation of the device is as follows:

If a drawing operation is to be eflected, the workpiece I96 is placed on the bed I and the hydraulic pump 23 is started and its control set so that fluid pressure passes through the conduit 2|. The plunger 1 first moves downwardly by gravity and the space above the plunger is filled by fluid from the pump 23 and ity and fluid from the variable delivery pumps I02 (Figure 3) or the variable delivery pump I42 (Figure 4) flows through the conduit 26 or conduits I03a and 26a respectively into the clamping cylinders. The cushioning cylinders 91 are assumed to have been fllled with fluid during the previous retraction stroke, so that III-- their cushioning plungers are in their upper position.

During the downward movement of the plunger 1 the liquid in the lower portion. of the main cylinder 5 escapes through the conduit 25 to the suction side 24 of the pump 23. As soon as the upper die 9 contacts the workpiece I96, pressure starts to build up in the main cylinder 5 above the plunger 1 and acts through the conduits 2| and 54 upon the.piston 66 of the valve member thereby moving the valve member 65 against the thrust of the spring 62 'toward the left so as to effect communication between the conduit 54 and the channel 53. Furthermore, the pressure in conduit 88 supported by the spring 18 moves the piston 11 upward while the spring 8| of the surge valve 1| moves the piston 80 engaged thereby likewise upward so as to close ass ses communication between th conduit 88 and the conduit 69. Just before the upper die 9 contacts the workpiece I96, the pins 90, 8| of the arm 82 engage the groove 88 of the cam 86 and move the rod 40 downwardly so as to shift the pistons 38 and 42 of the two-way valve 28 for interrupting the communication between the conduits 21 and 43. It will be understood that the rod 40 was previously held inits upper position by friction between the rod 40 and the packing material 3|, 32 surrounding the same. When the pistons 38 and 42 have reached their lower-most position while the downward movement of the die 8 still continues, the pins 90 and 9| click out of the groove 88, slide over cam 81 and at the end of the pressing or drawing operation are below the cam 81. When the drawing operation proper starts, the die 9 presses the workpiece I96 into the lower die against the resistance of the liquid in the cushioning cylinders 91. Fluid from the cushioning cylinders 91 can escape only through the relief valves I65 and the pressure in each cylinder 91 can be controlled by the adjustment of its respective relief valve, i. e. by setting the screw I96 of the valve I65.

After the upper die 9 has moved the desired distance and completed its drawing operation the flow through the pump 23 is reversed by any desired means so as to initiate the retraction stroke of the plunger 1. When the pins 90, 9| during this retraction stroke engage the groove 89 of the cam 81, they move the control rod 48 and the pistons 38, 42 in the two-way valve 28 to their uppermost position indicated in Figure 1, thereby establishing communication between the conduits 21 and 48 so that liquid from the clamping cylinder 6 may escape through the conduits 21, the check valves 29, the two-way valve 28, and the conduit 43 into the fluid tank 44. When the retraction stroke of the plunger 1 is about to be started, pressure fluid is delivered by the pump 23 into the conduit 25. However, at this time the piston prevents communication between the conduit 2| and the conduit 69 so that no fluid may escape through these conduits from the upper portion of the main cylinder 5. The pressure in the conduit 25 is therefore conveyed through the'conduit 55 and moves the pistons 58 and 41 of the valve 45 toward the left. Since previously the piston 66 was moved toward the left, fluid from the upper portion of the main cylinder 5 may now escape through the conduits 2|, 54 and 56 into the cylinder bore 49 from where it flows through the apertures 59 into the tank 44. Furthermore, liquid may escape from the conduits 2|, 54 and 56 into the cylinder bore 49 and from there'through the channel 53 and the aperture 52 into the tank 44.

The relief of pressure from the upper portion of the main cylinder 5 through the valve 46 enables the pressure in the conduit 55 to move the piston 11 of the surge valve 1| downwardly so as to push the piston 80 against the thrust of the spring 8|, thereby eifecting communication between the conduit 2| and the conduit 69 so that the liquid from the upper portion of the main cylinder 5 may now escape through the last-mentioned conduits into the surge tank. The pressure fluid delivered by the pump 23 through the conduit 25 into the lower portion of the main cylinder 5 now moves the plunger 1 upwardly. A portion of the pressure fluid also flows from the port-24 through the conduit 25a into the cushioning cylinders 91 so as to fill the latter and to raise the cushioning plungers 98 to the position "members for holding they occupy at the beginning of the drawing operation.

As previously mentioned, when the fluid pressure in the clamping cylinders 6 exceeds a predetermined pressure, the delivery of the pump I02 is automatically restricted so that the desired pressure is substantially maintained. If for some reason during the drawing operation the pressure in the clamping cylinders should still exceed a predetermined value, the respective check valves 29a come into operation so as to release the pressure until it again reaches the allowable value. As will be clear from the foregoing description, each clamping cylinder is individually controlled and may be individually adjusted according to the desired pressure in the respective clamping cylinder. A similar automatic control of the clamping cylinders is effected when the pumps I02 in the circuit of Figure 3 are replaced by the reducing valves l3! shown in Figure 4. In the latter case only one pump, viz. pump I42, supplies fluid to the clamping cylinders, and the pressure reducing valves l3l automatically maintain the desired individual pressures in the clamping cylinders 8a according to the setting of the respective springs ISO in the pressure reducing valves l3|,- as previously explained. The relief valves I88 associated with the cushioning cylinders prevent undue pressure in the cushioning cylinders, which pressure may be determined for each cushioning cylinder individually by the setting of the respective springs I90,

It will'be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims and the invention. For instance, if desired, the check valves 29 and 29a may be replaced by check valves in which the closure member is normally held in closed position by a spring. Also a constant delivery pump may be substituted for the variable delivery pump I42 or, preferably, the pump M2 with the conduit 3a and check valve "2a may be replaced by the self-controlling variable delivery pump 02.

Having thus fully described my invention what- I claim as new and desire to secure by Letters Patent is:

1. A hydraulic press comprising in combination a drawing plunger, means for actuating said drawing plunger, a plurality of clamping members operable by pressure fluid independently of each other for holding a workpiece clamped during the drawing operation of said drawing plunger, a. fluid source, and means associated with said clamping members including an individual pump as the sourceotpressure for each clamping member and means for normally exhausting the discharge from the pump for automatically and independently of the travel of said drawing plunger to control the supply of pressure fluid from said fluid source to said clamping members so as to allow the creation of different predetermined pressures on separate clamping members at one and the same time.

2. A hydraulic press comprising in combination a drawing plunger, means for actuating said plunger, a plurality of fluid operable clamping a workpiece during the drawing operation of said drawing plunger, -a fluid source, means respectively associated with said clamping members including an individual pump as the source of pressure for each clamping member and means for normally exhausting the discharge from the pump for automatically and independently of each other and of the travel of said drawing plunger to control the supply of fluid from said fluid source to the respective clamping member to create said predetermined pressures on diflerent clamping members, and means adapted to prevent equalization of the fluid pressure on said clamping members.

3. A hydraulic press-comprising in combination a drawing plunger, means for reciprocating said plunger, a plurality of fluid operable clamping members operable independently of each other to hold a workpiece during the drawing operation of said drawing plunger, a fluid source for supplying fluid to said clamping members including an individual pump as the source of pressure for each clamping member and means for normally exhausting the discharge from the pump for respectively and automatically to maintain predetermined diflerent minimum pressures on said clamping members independently of the travel of said drawing plunger, fluid operable cushionin members adapted to cooperate with said drawing plunger, and means adapted to control the pressure on said cushioning members independently of each other.

4. A hydraulic press comprising in combination a drawing plunger, means for actuating said plunger, a plurality of fluid operable clamping members reciprocable in clamping cylinders, pressure reducing valves respectively associated with said clamping cylinders, said pressure reducing valves being adapted automatically to restrict the flow of pressure fluid to their respective clamping cylinders in response to a predetermined pressure in said cylinders, pumping means communicating with each of said pressure reducing valves for supplying fluid therethrough to said cylinders, and means associated with said pumping means and responsive to a predetermined pressure in said cylinders for preventing further supply of fluid to said pressure reducing valves. V

5. A hydraulic press comprising in combination a main cylinder, a drawing plunger reciprocable in said main cylinder and carrying a control member, a variable delivery pump adapted to supply fluid to said main cylinder to actuate said drawing plunger, a plurality of fluid operable clamping members for holding a workpiece during the drawing operation of said drawing plunger, pumping means, independent of said variable delivery pump, for supplying fluid to said clamping members. and means respectively associated with said clamping members and adapted automatically and independently of each other and of the drawing action of said drawing plunger to vary the supply of pressure fluidto the respective clamping member and to maintain a predetermined minimum pressure thereon.

6. A hydraulic press comprising in combination a drawing plunger, a pump for supplying fluid to said drawing plunger for actuating the same, a plurality of fluid operable clamping cylinders, separate pumping means independent of said pump, one for each clamping cylinder, and adapted to supply fluid to said clamping cylinders, and means associated with said pumping means normally exhausting the discharge fluid therefrom and adapted respectively and at one and the same time to cause supply of difierent pressures to maintain the same in said clamping cylinders independently of the travel of said drawing plunger.

WALTER- ERNST. 

